Candito is not addressing the biomechanics of Rip's squat model; he's addressing the biomechanics of a learning progression drill. This is brainless. Don't get sucked in by fairly bright dudes making bait & switch arguments like this. Candito knows he's doing this bullshit, and it's cheap & easy marketing.
The point of Rip's hip drive drill is to get the body accustomed to recruiting the proper muscles, namely the posterior chain muscles. At this point in the learning progression, knee vs hip extension hasn't even been addressed. Hell...there isn't even a barbell in play at this stage of learning. What's important at this stage is that clients feel the ass and hamstrings at work.
At a later stage, emphasis will be placed on maintaining a solid torso angle out the bottom of a squat (ie...not letting the torso collapse to horizontal), thus assuring proper knee & hip extension with an emphasis on maintaining hamstring tension.
Rip is a world class coach. I've worked with many world class coaches, and at the SS Seminar I was simply awed by Rip's ability to get regular, spazzy people to perform flawless, complex biomechanical feats. You don't get people to move in accord with a biomechanical model by getting them to cognate on biomechanics...you use appropriate drills & cues to get the body to move properly. This is art and complex communication at its best.
Of course the biomechanics of the hip drive drill are fucked up! it's a drill. And it's also a near-magical way to get inexperienced people to feel hip drive. It's the sort of drill employed by someone who's coached for decades and got hundreds of thousands (probobly miliions) of folks very strong.
Rip certanly doesn't need me defending him, but I'm just so sick of how much bullshit exists in the fitness industry.